1. Field of the Invention
This invention generally relates to a method of controlling a sheet metal machining line for producing desired products by cutting, drilling, bending and/or otherwise machining flat workpieces according to a machining schedule prepared on the basis of a given production plan. More particularly, the invention relates to a method of controlling a sheet metal machining line designed to foresee an unfavorable situation that can force the operation of the line of manufacturing products of a specific item to be suspended for reasons, such as no available workpieces and/or a preparatory work to be done such as an exchange of metal molds, that can arise before or during the machining operation for the products. The control method includes analyzing the unit machining schedule or schedules for the products including the data items described in the schedule or schedules, such as the identification numbers of the machining programs involved, the use or non-use of such identification numbers, the number of workpieces to be machined and the presence or absence of the predetermined procedures for exchanging metal molds to be referred to for manufacturing the products, and informing the operator of the foreseen situation or the non-existence of such a foreseen unfavorable situation in order to make the operator prepared for a possible suspension of the operation of the line.
The present invention also relates to an apparatus for controlling a sheet metal machining line by using such a control method.
2. Background Information
Automated power saving manufacturing systems such as flexible manufacturing system (FMS) have been known and in popular use in sheet metal machining lines for cutting, drilling, bending and otherwise treating sheet metals into intended products.
An apparatus for controlling a sheet metal machining line utilizing an FMS system will be summarily described. A sheet metal machining line typically comprises an NC machining center including one or more punch presses adapted to selectively use a plurality of metal molds and tools, a CNC control apparatus for controlling the operation of the NC machining center according to a machining program, a workpiece holding/releasing unit for holding one or more workpieces to be machined in position relative to the NC and releasing them for delivery, an automatic warehouse for sorting a large number of workpieces into groups of same materials and sizes and storing them for future machining, peripheral equipment including one or more cranes and other devices for feeding workpieces to the workpiece holding/releasing unit from the automatic warehouse, and a line control board connected to the NC machining center, the CNC control apparatus and the peripheral equipment for controlling the sequence of operations of the sheet metal machining line. The sheet metal machining line is additionally connected to a cell controller for transferring machining programs to the CNC control apparatus and also transferring ladder-sequence programs to the line control board in order to control the entire operation of the sheet metal machining line in a coordinated manner.
The cell controller is connected to a hard disc memory device having a predetermined capacity typically for storing machining schedules prepared according to a given production plan describing the operating procedures of the NC machining center and the peripheral equipment for sequentially producing products according to the production plan. The cell controller sequentially issues commands for operation according to the machining schedule and the issued operational commands are then sent to the CNC control apparatus and the line control board. Upon receiving the commands, the sheet metal machining line sequentially carries out the specified machining operations including cutting, drilling and bending on the delivered flat workpieces.
A machining schedule typically comprises one or more unit machining schedules designed for each specific product item and arranged, if more than one unit machining schedule is used, in the order of the machining operations to be carried out.
The machining schedule describes data items such as the identification numbers of the machining programs involved, the use or non-use of such identification numbers, the number of workpieces to be machined the presence or absence of the predetermined procedures for exchanging metal molds, and completion codes for indicating the completion of the operations specified in the unit machining schedule. The cell controller causes the predetermined machining operations to be carried out in the order defined by the machining schedule by referring to the machining schedule whenever necessary so that groups of products may be produced according to the machining schedule.
However, a known apparatus for controlling a sheet metal machining line having a configuration as described above can inevitably be brought into a situation that can arise before or during the machining operation conducted according to a unit machining schedule to force the operation of the line of manufacturing products of a specific item to be suspended. Such a situation may be that the number of available workpieces is short of the number of workpieces to be machined, that the machining operations for the current unit machining schedule are over but the machining program required for carrying out the next unit machining schedule is not at hand or that there is preparatory work to be done by the operator such as an exchange of metal molds. A very skilled operation may not be able to foresee the time when the line is suspended due to such a situation. Therefore, there is a need for technological development that can solve this problem.
Thus, the operator is currently required to constantly watch the sheet metal machining line and also respond to unusual conditions that may require the preparation of an additional machining program, an additional supply of workpieces and/or the performance of preparatory work for exchanging metal molds. Constantly watching the sheet metal machining line and concurrently carrying out a preparatory work at the same time can constitute an extraordinary heavy workload for the operator both physically and mentally. In view of the above circumstances, it has been desired to provide a novel technological development that can foresee an unfavorably situation that can force the operation of the sheet metal machining line to be suspended and to notify the operator of the foreseen situation well before the start of the operation.